goofy&gooftool: Fix unused variable names.

The "dummy_" is deprecated by "unused_".

BUG=none
TEST=make lint # no more W0613 in goofy and gooftool.

Change-Id: Ieb7cf4fb06a9bcf4cbef8eeda64c90903e7fcf08
Reviewed-on: https://chromium-review.googlesource.com/202482
Reviewed-by: Ricky Liang <jcliang@chromium.org>
Tested-by: Hung-Te Lin <hungte@chromium.org>
diff --git a/py/gooftool/gooftool.py b/py/gooftool/gooftool.py
index 971197c..674c73a 100755
--- a/py/gooftool/gooftool.py
+++ b/py/gooftool/gooftool.py
@@ -669,7 +669,7 @@
   VerifyBranding(options)
 
 @Command('untar_stateful_files')
-def UntarStatefulFiles(dummy_options):
+def UntarStatefulFiles(unused_options):
   """Untars stateful files from stateful_files.tar.xz on stateful partition.
 
   If that file does not exist (which should only be R30 and earlier),